The applicants long-term objective is to obtain a detailed understanding of the functioning of human embryonic haemoglobins and, in so doing, to gain an insight into the normal behavior of the oxygen transport system which operates at the earliest stages of human development. This data will provide valuable parameters related to the physiology and development of the early human individual. There are three specific aims which constitute this project namely (i) the preparation, from nonembryonic sources, of a yeast system capable of expressing, in high yields, functional forms of each of the three human embryonic haemoglobins; (ii) the isolation of purified haemoglobins to be used in oxygen binding equilibrium and kinetic investigations of the protein function; directed towards the identification of the factors controlling their interactions with and (iii) the crystallization and subsequent three dimensional structure determination of each haemoglobin so allowing the rationalization of the functional properties of these proteins at the molecular level.